First the QB no matter who it is needs to have a line to pass protect. The Giants have not wanted to address that for years. Manning has only had a few really good years. To many years of some real good games along then with some terrible games with some so so games. Manning was never his brother. It really would not have mattered if he was the last few years because of the poor line blocking and the Giants never making a priority to upgrade the offensive line. Just because he was on 2 Super Bowl teams never meant he was a Super QB.
Beckham has to many child tantrums after he got a hugh contract. Great talent and great headache.